Wheat, corn, rice, soybean, etc., are important crops, and a variety of herbicides have been used to achieve an increase in yields of these crops. However, conventional herbicides are hardly satisfactory in respect of herbicidal activity and safety for crops. It is desired to develop a safe herbicide which kills detrimental weeds in a small dosage, and shows no phytotoxicity to crops.
As such a herbicide, Japanese Laid-Open (Kokai) Patent Publication No. 10779/1988 (Sho 63-10779) discloses and proposes compounds of the following formula (IA) ##STR1## wherein Ar.sup.o is a group of the formula, ##STR2## in which R.sup.11 to R.sup.13 and R.sup.15 to R.sup.19 are the same as or different from each other and each is a hydrogen atom, a methyl group or an ethyl group, and each of R.sup.14 and R.sup.20 is a hydrogen atom, a hydroxyl group, a methyl group, a methoxy group or an ethoxy group, and
R.sup.o is a methyl group or a methoxy group.
Japanese Laid-Open (Kokai) Patent Publication No. 201180/1988 (Sho 63-201180) discloses a herbicidal composition comprising, as active ingredients, at least one compound selected from the group of urea derivative compounds of the following formula (IB) ##STR3## wherein:
Ar' is a group of the formula ##STR4## wherein R.sup.21 to R.sup.35 are the same as or different from each other and each is a hydrogen atom, a lower alkyl group or a lower alkoxyl group, R.sup.36 is a hydrogen atom, a lower alkyl group, a lower alkoxy group or a hydroxyl group provided that R.sup.22 and R.sup.23, R.sup.26 and R.sup.27, R.sup.29 and R.sup.30, R.sup.31 and R.sup.33, or R.sup.33 and R.sup.35 may be bonded to each other to form an alkylene chain optionally substituted with a lower alkyl group and may form a 5- or 6-membered ring together with carbon atoms to which these groups are bonded, or R.sup.31 and R.sup.32 may be bonded to each other to form an ethylenedioxyl group, or R.sup.34 and R.sup.35 may be bonded to each other to form a dichloromethylene group, A is a nitrogen atom or ##STR5## in which X is a hydrogen atom, a chlorine atom, a nitro group or a trifluoromethyl group, and B is a hydrogen atom, a methyl group or a methoxy group, and at least one compound selected from the group consisting of the following compounds (2A) to (2P): (2A) 4-chlorobutyn-2-yl N-(3-chlorophenyl)carbamate, (2B) 1,2-dimethyl-3,5-diphenyl-1H-pyrazolium methylsulfate, (2C) methyl 2-[4-(2,4-dichlorophenoxy)phenoxy]propionate, (2D) 3-(4-isopropylphenyl)-1,1-dimethylurea, (2E) 3-(3-chloro-4-methylphenyl)-1,1-dimethylurea, (2F) ethyl 2-[N-benzoyl-N-(3,4-dichlorophenyl)amino]propionate, (2G) S-2,3,3-trichloro-2-propenyl-N,N-diisopropylthiocarbamate, (2H) 4-hydroxy-3,5-diiodobenzonitrile, (2I) 2-chloro-N-(4-methoxy-6-methyl-1,3,5-triazin-2-ylaminocarbonyl)benzene sulfonamide, (2J) 3-(2-benzothiazolyl)-1,3-dimethylurea, (2K) 2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine, (2L) 2-(4-chloro-6-ethylamino-1,3,5-triazin-2-yl)amino-2-methylpropionitrile, (2M) 2-(3,5-dichlorophenyl)-2-( 2,2,2-trichloroethyl)oxirane, (2N) 2-chloro-2'-ethyl-N-(2-methoxy-1-methylethyl)-6'-methylacetanilide, (20) 2-chloro-2',6'-diethyl-N-methoxymethylacetanilide, and (2P) 2-chloro-N-isopropyl-N-(3,3,5-trimethylcyclohexenyl)acetamide.
Further, the following compounds (3A) to (3P) are known to be herbicidally active compounds: (3A) 3-(5-tert-butyl-1,3,4-thiadiazolyl-2-yl)-1,3-dimethylurea, (3B) 1,3-dimethyl-3-(5-trifluoromethyl-1,3,4-thiadiazoyl-2-yl)urea, (3C) 1-(5-ethylsulfonyl-1,3,4-thiadiazoyl-2-yl)-1,3-dimethylurea, (3D) 3-(3,4-dichlorophenyl)-1,1-dimethylurea, (3E) 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea, (3F) 3,6-dichloro-2-methoxybenzoic acid, (3G) [(3,5,6-trichloro-2-pyridyl)-oxy]acetic acid triethylamine salt, (3H) 4-chloro-2-methylphenoxy acetic acid, (3I) 2-(4-chloro-2-methylphenoxy)propionic acid, (3J) 4-amino-3,5-dichloro-6-fluoro-2-pyridyloxy acetic acid, (3K) isopropyl N-(3-chlorophenyl)carbamate ester, (3L) N,N-diethylthiolcarbamic acid-S-(2-chlorobenzyl)ester, (3M) 2-methylthio-4-isopropylamino-6-methylamino-1,3,5-triazine, (3N) 2-chloro-4,6-bis(ethylamino)-1,3,5-triazine, (30) 4-amino-6-tert-butyl-3-methylthio-1,2,4-triazin-5(4H)-one, and (3P) 3 -isopropyl-1H-2,1,3-benzothiazin-4(3H)-one-2,2-dioxde.
However, the above compound (1A) and the above compounds (3A) to (3P) have drawbacks that when these compounds are used alone, they have an effect on controlling various weeds only when used in a high dosage, but use of them in a low dosage is limited to very small kind of controllable weeds. These drawbacks remain to be solved.
The above Japanese Laid-Open Patent Publication discloses the following: The composition comprising a combination of the above compound (1B) with one of the compounds (2A) to (2P) is a composition comprising a combination of the compound (1B) which is not necessarily sufficient in the herbicidal activity against gramineous weeds such as wild oat, blackgrass, etc., with one of the compounds (2A) to (2G), (2J) and (2M) to (2P) which are excellent in the herbicidal activity against these gramineous weeds, with one of the compounds (2H) and (2I) which are excellent in the herbicidal activity against broad-leaved weeds, or with one of the compounds (2K) and (2L) which are excellent in the herbicidal activity against annual broad-leaved weeds and some gramineous weeds, and the composition comprising one of the above combinations exhibits a herbicidal effect that cannot be obtained when the above compounds are used alone.